Clinical Biomechanics - Articles in Press

Biomechanical evaluation of double bundle augmentation of posterior cruciate ligament using finite element analysis - Corrected Proof

Kyoung Ho Yoon, Yoon Hyuk Kim, Jeong Han Ha, Kyungsoo Kim, Won Man Park — 2010-09-03

Abstract: Background: Posterior cruciate ligament injuries commonly occur during sports activities or motor vehicle accidents. However, there is no previous comparison study of single bundle reconstruction, double bundle reconstruction, and double bundle augmentation with respect to biomechanical characteristics such as stability and ligament stress.Methods: A three-dimensional finite element model of a lower extremity including femur, tibia, cartilage, meniscus, collagen fibers, and four major ligaments was developed and validated. In addition to the intact, posterior cruciate ligament injured, single bundle reconstruction, double bundle reconstruction, and double bundle augmentation models were developed. Then, the posterior and rotational tibial translations as well as the ligament stresses were predicted for 89N posterior force and 3Nm internal torque, respectively, in the normal (no secondary deficiency) and the secondary deficiency cases using finite element analysis.Findings: The posterior stability and ligament stresses following double bundle augmentation were superior to those of single and double bundle reconstructions, especially after secondary deficiency in the reconstructed grafts, despite little difference in posterior stability between double bundle reconstruction and augmentation in the normal case. Similarly, the double bundle augmentation had the greatest rotational stability while there was little advantage in ligament stress compared to those of the other reconstruction method.Interpretation: Double bundle augmentation has advantages with regard to posterior and rotational stabilities as well as ligament stress in comparison with other reconstruction methods, especially following secondary deficiencies in the reconstructed grafts.

Stride-to-stride variability is altered during backward walking in anterior cruciate ligament deficient patients - Corrected Proof

2010-09-02

Abstract: Background: Recently backward walking is used by physical therapists to strengthen the hamstring muscles and thus improve the function of the knee joint of anterior cruciate ligament deficient patients. The aim of this study was to examine the stride-to-stride variability of anterior cruciate ligament deficient patients during backward walking. The variation of how a motor behavior emerges in time is best captured by tools derived from nonlinear dynamics, for which the temporal sequence in a series of values is the facet of interest.Methods: Fifteen patients with unilateral anterior cruciate ligament deficiency and eleven healthy controls walked backwards at their self-selected speed on a treadmill while three-dimensional knee kinematics were collected (100Hz). A nonlinear measure, the largest Lyapunov Exponent was calculated from the resulted knee joint flexion–extension data of both groups to assess the stride-to-stride variability.Findings: Both knees of the deficient patients exhibited significantly lower Lyapunov Exponent values as compared to the healthy control group revealing more rigid movement pattern. The intact knee of the deficient patients showed significantly lower Lyapunov Exponent values as compared to the deficient knee.Interpretation: Anterior cruciate ligament (ACL) deficiency leads to loss of optimal variability regardless of the walking direction (forwards in previous studies or backwards here) as compared to healthy individuals. This could imply diminished functional responsiveness to the environmental demands for both knees of ACL deficient patients which could result in the knees being more susceptible to injury.

Effect of an anterior-sloped brace joint on anterior tibial translation and axial tibial rotation: A motion analysis study - Corrected Proof

C.H. Yeow, W.L. Gan, P.V.S. Lee, J.C.H. Goh — 2010-08-27

Abstract: Background: Anterior tibial translation and axial tibial rotation are major biomechanical factors involved in anterior cruciate ligament injuries. This study sought to evaluate a brace prototype designed with an anterior-sloped joint, in terms of its efficacy in attenuating anterior tibial translation and axial tibial rotation during landing, using a motion analysis approach.Methods: Ten healthy male subjects performed single-leg landing tasks from a 0.6-m height with and without the brace prototype. Ground reaction force and kinematics data were obtained using a motion-capture system and force-plates. Anterior tibial translation and axial tibial rotation were determined based on tibial and femoral marker reference frames. Vertical and anterior–posterior ground reaction forces, hip, knee and ankle joint range-of-motions and angular velocities, anterior tibial translation and axial tibial rotation were compared between unbraced and braced conditions using Wilcoxon signed-rank test.Findings: We found no significant difference in peak vertical and anterior–posterior ground reaction forces (p=0.770 and p=0.332 respectively) between unbraced and braced conditions. Knee joint range-of-motion and angular velocity were lower (p=0.037 and p=0.038 respectively) for braced condition than unbraced condition. Anterior tibial translation and axial tibial rotation were reduced (p=0.027 and p=0.006 respectively) in braced condition, compared to unbraced condition.Interpretation: The anterior-sloped brace joint helps to attenuate anterior tibial translation and axial tibial rotation present in the knee joint during landing. It is necessary to test the brace prototype in a sporting population with realistic sports landing situations in order to assess its effectiveness in lowering anterior cruciate ligament injury risk.

The association between lower extremity energy absorption and biomechanical factors related to anterior cruciate ligament injury - Corrected Proof

Marc F. Norcross, J. Troy Blackburn, Benjamin M. Goerger, Darin A. Padua — 2010-08-27

Abstract: Background: Greater total energy absorption by the lower extremity musculature during landing may reduce stresses placed on capsuloligamentous tissues with differences in joint contributions to energy absorption potentially affecting anterior cruciate ligament injury risk. However, the relationships between energy absorption and prospectively identified biomechanical factors associated with non-contact anterior cruciate ligament injury have yet to be demonstrated.Methods: Sagittal plane total, hip, knee and ankle energy absorption, and peak vertical ground reaction force, anterior tibial shear force, knee flexion and knee valgus angles, and internal hip extension and knee varus moments were measured in 27 individuals (14 females, 13 males) performing double leg jump landings. Correlation coefficients assessed the relationships between energy absorption during three time intervals (initial impact phase, terminal phase, and total landing) and biomechanical factors related to anterior cruciate ligament injury.Findings: More favorable values of biomechanical factors related to non-contact anterior cruciate ligament injury were associated with: 1) Lesser total (R2=0.178–0.558), hip (R2=0.229–0.651) and ankle (R2=0.280), but greater knee (R2=0.147) energy absorption during the initial impact phase; 2) Greater total (R2=0.170–0.845), hip (R2=0.599), knee (R2=0.236–0.834), and ankle (R2=0.276) energy absorption during the terminal phase of landing; and 3) Greater knee (R2=0.158–0.709), but lesser hip (R2=0.309) and ankle (R2=0.210–0.319) energy absorption during the total landing period.Interpretation: These results suggest that biomechanical factors related to anterior cruciate ligament injury are influenced by both the magnitude and timing of lower extremity energy absorption during landing.

Does cancellous bone compaction due to insertion of a blade implant influence the cut-out resistance? A biomechanical study - Corrected Proof

Dirk Wähnert, Paata Gudushauri, Damiano Schiuma, Geoff Richards, Markus Windolf — 2010-08-27

Abstract: Background: For the treatment of hip fractures helically shaped implants, like the Dynamic Hip Screw (DHS) Blade, are often used. One consequence of blade implantation, the compaction of cancellous bone, is still believed to increase cut-out resistance. This in vitro study investigates implant anchorage of Dynamic Hip Screw Blades in femoral heads due to insertion with or without predrilling under cyclic physiological loading conditions.Methods: Six pairs of fresh frozen (−20°C) human cadaveric proximal femora were instrumented with DHS Blades. Bone pairs were randomly assigned to two study groups: 1) predrilled; 2) non-predrilled. Prior instrumentation, bone mineral density was determined in the center of the femoral head by Xtreme-CT measurement. After instrumentation biomechanical testing was performed under cyclic loading. The bone-implant interface was monitored by means of fluoroscopic imaging throughout the experiment. Paired t-tests were performed to identify differences regarding bone mineral density, stiffness and cycles to failure.Findings: No significant differences were found between study groups with regard to axial stiffness (P=0.626) and number of cycles to failure (P=0.961).Interpretation: This in vitro study did not show differences in biomechanical stability of proximal femora instrumented with a helical blade implant with or without predrilling. Clinically, the findings suggest that predrilling may be performed to ease the surgical procedure without compromising the implant anchorage.

Healing of a painful intervertebral disc should not be confused with reversing disc degeneration: Implications for physical therapies for discogenic back pain - Corrected Proof

Michael A. Adams, Manos Stefanakis, Patricia Dolan — 2010-08-26

Abstract: Background: Much is known about intervertebral disc degeneration, but little effort has been made to relate this information to the clinical problem of discogenic back pain, and how it might be treated.Methods: We re-interpret the scientific literature in order to provide a rationale for physical therapy treatments for discogenic back pain.Interpretation: Intervertebral discs deteriorate over many years, from the nucleus outwards, to an extent that is influenced by genetic inheritance and metabolite transport. Age-related deterioration can be accelerated by physical disruption, which leads to disc “degeneration” or prolapse. Degeneration most often affects the lower lumbar discs, which are loaded most severely, and it is often painful because nerves in the peripheral anulus or vertebral endplate can be sensitised by inflammatory-like changes arising from contact with blood or displaced nucleus pulposus. Surgically-removed human discs show an active inflammatory process proceeding from the outside-in, and animal studies confirm that effective healing occurs only in the outer anulus and endplate, where cell density and metabolite transport are greatest. Healing of the disc periphery has the potential to relieve discogenic pain, by re-establishing a physical barrier between nucleus pulposus and nerves, and reducing inflammation.Conclusion: Physical therapies should aim to promote healing in the disc periphery, by stimulating cells, boosting metabolite transport, and preventing adhesions and re-injury. Such an approach has the potential to accelerate pain relief in the disc periphery, even if it fails to reverse age-related degenerative changes in the nucleus.

Alterations in neuromuscular patterns between pre and one-year post-total knee arthroplasty - Corrected Proof

2010-08-23

Abstract: Background: Total knee arthroplasty is a common treatment for severe knee osteoarthritis. Objective measures are needed to evaluate the effect of arthroplasty surgery on function and joint loading, in particular given the rise in younger adults receiving this intervention. The objective was to compare neuromuscular activation patterns of the knee musculature during level walking one-week prior to and one-year following total knee arthroplasty.Methods: Surface electromyograms from seven periarticular muscles were recorded from 43 patients with severe medial compartment knee osteoarthritis during walking one-week prior to and one-year following total knee arthroplasty. Principal component analysis extracted patterns from the electromyographic waveforms and assigned scores for these patterns, which were statistically compared between test times and between medial and lateral sites within a muscle group.Findings: Significantly lower overall activation amplitudes were found for the quadriceps and hamstrings, with decreased activity during mid-late stance following surgery. Significant increases in gastrocnemius activity were found late stance, along with altered waveform shapes.Interpretation: In general, the post-surgical changes moved toward more typical asymptomatic patterns, supporting improved neuromuscular strategies during walking. Given that improvements would not be expected to occur naturally in severe osteoarthritic knees the positive changes in neuromuscular characteristics during specific phases of the gait cycle can be explained in part by the altered mechanical environment and reduction in pain from the surgical intervention. These objective findings are directly relevant to the joint loading environment and can be valuable for evaluating surgical techniques, different prostheses and pre–post surgical management.

Gender differences in lower extremity gait biomechanics during walking using an unstable shoe - Corrected Proof

Benno M. Nigg, Karelia E. Tecante G., Peter Federolf, Scott C. Landry — 2010-08-23

Abstract: Background: In recent years several unstable shoe designs that cause increased instability at the ankle joint have been developed with the aims of training static and dynamic posture and postural control. However, earlier research found significant gender differences in the generation of ankle torque and in the reaction times after a perturbation. Therefore it is possible that men and women are affected differently by the instability that unstable shoes create. The purpose of this study was to investigate if gender differences exist a) during bilateral quiet stance or b) in lower extremity gait kinematics and kinetics when using unstable shoes.Methods: Seventeen females and seventeen males were included in this study. Masai Barefoot Technology® shoes were used as test shoes. Center of pressure excursion was recorded during 30s bilateral quiet stance trials using a force plate. Joint angles, resultant joint moments and joint moment impulses during walking were determined using standard gait analysis methods.Findings: In bipedal stance, female subjects had significantly greater anterior–posterior center of pressure excursion than male subjects. In the stance phase of the gait cycle gender differences were found in the ankle joint moments which had not been reported in earlier studies using barefoot or normal shoe conditions.Interpretation: The results suggest that women and men use different strategies to control the ankle joint when standing or walking in unstable shoes. Gender effects should therefore be taken into consideration if functional or therapeutic effects of unstable shoes are assessed.

Age-related differences in lower-limb force–time relation during the push-off in rapid voluntary stepping - Corrected Proof

I. Melzer, T. Krasovsky, L.I.E. Oddsson, D.G. Liebermann — 2010-08-20

Abstract: Background: This study investigated the force–time relationship during the push-off stage of a rapid voluntary step in young and older healthy adults, to study the assumption that when balance is lost a quick step may preserve stability. The ability to achieve peak propulsive force within a short time is critical for the performance of such a quick powerful step. We hypothesized that older adults would achieve peak force and power in significantly longer times compared to young people, particularly during the push-off preparatory phase.Methods: Fifteen young and 15 older volunteers performed rapid forward steps while standing on a force platform. Absolute anteroposterior and body weight normalized vertical forces during the push-off in the preparation and swing phases were used to determine time to peak and peak force, and step power. Two-way analyses of variance (‘Group’ [young–older] by ‘Phase’ [preparation-swing]) were used to assess our hypothesis (P≤0.05).Findings: Older people exerted lower peak forces (anteroposterior and vertical) than young adults, but not necessarily lower peak power. More significantly, they showed a longer time to peak force, particularly in the vertical direction during the preparation phase.Interpretations: Older adults generate propulsive forces slowly and reach lower magnitudes, mainly during step preparation. The time to achieve a peak force and power, rather than its actual magnitude, may account for failures in quickly performing a preventive action. Such delay may be associated with the inability to react and recruit muscles quickly. Thus, training elderly to step fast in response to relevant cues may be beneficial in the prevention of falls.

Experimental calf muscle pain attenuates the postural stability during quiet stance and perturbation - Corrected Proof

Rogério Pessoto Hirata, Lars Arendt-Nielsen, Thomas Graven-Nielsen — 2010-08-09

Abstract: Background: The purpose of this study was to evaluate how acute pain changes the postural control and stability during quiet standing and after unexpected perturbations.Methods: Nine subjects stood as quiet as possible on a movable force platform that recorded the centre of pressure position and provided unexpected floor perturbations, before, during and after experimental calf muscle pain. Bilateral surface electromyography from the tibialis anterior and medial gastrocnemius muscles was recorded. The foot pressure distributions were measured using pressure insoles. Intramuscular injections of hypertonic saline were administrated (right leg) to induce acute pain in the tibialis anterior and/or medial gastrocnemius muscles, and an isotonic injection was used as control.Findings: Simultaneous pain in tibialis anterior and medial gastrocnemius altered the postural control. During quiet standing: higher medial-lateral centre of pressure speed and increased total sway displacement (P<0.05), weight moved to the non-painful side, (P<0.05) and plantar centre of pressure of the left foot was shifted towards the heel’s direction (P<0.05). During forward perturbation: higher mean displacement in the medial-lateral direction (P<0.05). After the perturbation: larger sway area (P<0.05). Pain only in the medial gastrocnemius muscle increased medial-lateral centre of pressure speed (P<0.05) during the quiet standing. Pain only in the tibialis anterior muscle increased peak pressure on the contralateral foot (P<0.05).Interpretation: These findings suggest that large acute painful areas on the calf muscles impair the postural control and potentially increase the risk factors for falls. Further strategies aiming to reduce pain in patients may lead to improvement in balance.

Knee biomechanics during walking gait following matrix-induced autologous chondrocyte implantation - Corrected Proof

Jay R. Ebert, David G. Lloyd, Timothy Ackland, David J. Wood — 2010-08-09

Abstract: Background: Matrix-induced autologous chondrocyte implantation is a technique for repairing articular cartilage defects in the knee. Despite reported improvements in pain, little is known about the recovery of knee biomechanics during walking gait.Methods: A randomized controlled study design was used to investigate knee biomechanics during gait in 61 patients following matrix-induced autologous chondrocyte implantation, in conjunction with either ‘accelerated’ or ‘traditional’ approaches to post-operative weight-bearing rehabilitation. Gait analysis was performed at 3, 6 and 12months post-surgery in both patient groups, and two matched, unaffected control groups for comparison.Findings: The spatiotemporal and ground reaction force parameters were similar between patient groups and their respective control groups at all time points. When compared with controls, both patient groups demonstrated significantly reduced knee extension moments up until, and including, 12months. The traditional group demonstrated a significantly reduced knee adduction moment at 3, 6 and 12months, and a significantly reduced knee flexion moment at 3months. There were no differences in these knee moments between the accelerated patient group and controls.Interpretation: Overall, a higher level of gait dysfunction was observed in patients who underwent traditional rehabilitation. Future research is needed to investigate the recovery of normal gait following matrix-induced autologous chondrocyte implantation, and its effect on repair tissue development.

Anatomical plate configuration affects mechanical performance in distal humerus fractures - Corrected Proof

Rainer Penzkofer, Sven Hungerer, Felix Wipf, Geert von Oldenburg, Peter Augat — 2010-08-09

Abstract: Background: Because of strong loads acting in the elbow joint, intraarticular fractures with a methaphyseal comminuted fracture site at the distal humerus demand a lot from the osteosynthetic care. Ambiguities arise concerning to the anatomic position of the implants and the resulting mechanic performance. The aim of this biomechanical study was to compare the performance of different anatomical plate configurations for fixation of comminuted distal humerus fractures within one system.Methods: In an artificial bone model two perpendicular and one parallel plating configuration of a dedicated elbow plating system were compared with respect to system rigidity (flexion and extension) and dynamic median fatigue limit (extension). The flexion tests were conducted under 75° and the extension tests under 5°. Furthermore, the relative displacements were recorded. As a fracture model an AO C 2.3-fracture on an artificial bone (4th Gen. Sawbone) was simulated via double osteotomy in sagittal and transversal plane.Findings: Large differences in mechanical performance were observed between flexion and extension loading modes. In extension the parallel configuration with lateral and medial plates achieved the highest bending stiffness and median fatigue limit. In flexion the highest bending stiffness was reached by the construct with a medial and a postero-lateral plate. Failure of the implant system predominantly occurred at the screw–bone interface or by fatigue of the plate around the screw holes.Interpretation: All three plate configurations provided sufficient mechanical stability to allow early postoperative rehabilitation with a reduced loading protocol. Although the individual fracture pattern determines the choice of plate configuration, the parallel configuration with lateral and medial plates revealed biomechanical advantages in extension only.

In vivo 3D kinematics of normal forearms: Analysis of dynamic forearm rotation - Corrected Proof

2010-08-09

Abstract: Background: Forearm rotation is an indispensable activity of daily living and comprises complex motions with rotational and translational components. It is thought that changes in these motions with injury or disease may affect diagnostic indices. Several studies have assessed in vivo forearm kinematics with static conditions, but dynamic forearm kinematics have not yet been reported. The purpose of this study was to analyze forearm kinematics during dynamic rotation using radiographic 3D–2D registration methods.Methods: Ten forearms of five healthy males with the mean age of 37years old were enrolled. Lateral fluoroscopic images were taken during forearm rotation from maximum supination to maximum pronation with their elbows flexed to approximately 45°. Geometric bone models were created from CT scans of the humerus, the radius and the ulna. Three-dimensional kinematics were determined using 3D–2D model registration techniques with the images and models, and the arc of axial rotation of the radius, volar/dorsal translation of the ulna at the distal radioulnar joint and rotation axis of forearm were computed.Findings: The radial rotation arc was 157°. The ulna translated 3.9mm (SD 1.5mm) dorsally during activity. The rotation axis of the forearm passed through the center of the radial head and the ulnar head at the 1.9mm (SD 0.7mm) posterior from its geometric centroid.Interpretation: The posteriorly deviated rotation axis at the ulnar head may result in the ulnar head translating dorsally during pronation. These data provide a basis for objective assessment of pathological forearm function.

A retrospective analysis of balance control parameters in elderly fallers and non-fallers - Corrected Proof

Itshak Melzer, Ilan Kurz, Lars I.E. Oddsson — 2010-08-09

Abstract: Background: A cross-sectional retrospective study of parameters reflecting balance function in elderly fallers and non-fallers was conducted to better understand postural control mechanisms in individuals prone to falls.Methods: Ninety-nine old adults (65–91years, mean age 78.4 (SD 5.7)) from two self-care residential facilities participated in the study. Foot center-of-pressure (CoP) displacement data were collected during narrow base upright stance eyes closed conditions and analyzed using summary statistics and Stabilogram-Diffusion Analysis (SDA) for mediolateral (ML) and anteroposterior (AP) directions. Subjects were instructed to minimize body sway.Findings: Twenty-nine of the subjects reported at least one fall and 69 subjects reported no falls in the past six months. The SDA showed significantly higher short-term diffusion coefficients and critical displacements in fallers in the ML but not the AP direction. Mean sway area and ML-CoP sway range were also larger in fallers.Interpretation: The greater ML critical displacement seen in fallers suggests that balance corrections on average occurred at higher sway amplitudes in this population. This is consistent with an ML decrease in the sensitivity of their postural control system. A higher short-term diffusion coefficient is consistent with increased muscle stiffness, a possible compensation for lost control sensitivity. Testing balance function under narrow stance conditions provides a modest increase in task difficulty that may help reveal pre-conditions of the balance control system that could increase the risk of falls.

Effects of maturation on the mechanical properties of regenerated and residual tissues in the rabbit patellar tendon after resection of its central one-third - Corrected Proof

2010-08-02

Abstract: Background: The central one-third portion of the patellar tendon is commonly used as a graft for the reconstruction of the anterior cruciate ligament. Although several studies have been carried out on mechanical properties of healing tendons in mature animals, there have been no studies on regenerated and residual tissues in the immature patellar tendon after the removal of its central portion.Methods: An entire one-third defect was made in the patellar tendon of 2-, 3- and 6-month-old rabbits. After 3 weeks, the tissue regenerated in the defect and the residual tissue were biomechanically and histologically evaluated.Findings: The length of patellar tendons in 6-month-old animals after the resection of its central one-third was significantly longer than that in age-matched controls. The cross-sectional area of all operated tendons was significantly larger compared to age-matched controls. There were no significant effects of maturation on the mechanical properties of regenerated and residual tissues in operated tendons, although tensile strength and tangent modulus of normal tendons were significantly greater in 6-month rabbits than in immature ones. The histology of each of regenerated and residual tissues was similar in the three groups.Interpretation: There were no remarkable effects of maturation on regenerated and residual tissues after the removal of the central one-third tendon. However, the strength and the modulus of normal tendons are significantly lower in immature patients than in mature ones. Therefore, surgeons should take account of the inferior mechanical properties of the tendon in skeletally immature patients at the time of surgeries for the reconstruction of the anterior cruciate ligament.

The role of strategy selection, limb force capacity and limb positioning in successful trip recovery - Corrected Proof

Paulien E. Roos, M. Polly McGuigan, Grant Trewartha — 2010-07-30

Abstract: Background: Fall occurrence, mainly due to tripping, increases with age. There are two main strategies of trip recovery: elevating and lowering. Strategy selection depends on trip stimulus timing within the swing phase of walking, but the choice and ultimate success of a strategy selection may also depend on individual physical characteristics.The aim of this study was to investigate: 1) recovery strategy choice by younger and older adults when perturbed in the ‘strategy overlap’ mid-swing phase, and 2) whether the interaction between recovery limb positioning and recovery limb force capacity determines recovery success in elevating strategy recoveries and accounts for strategy selection.Methods: A group of older (65–75years) and a group of younger adults (20–35years) completed a trip recovery protocol in a laboratory environment.An inverted pendulum model was developed to investigate how walking speed, recovery limb positioning and recovery limb force interacted and influenced successful trip recovery when perturbed in different swing phases.Findings: Older adults always adopted a lowering strategy when perturbed in late mid-swing (60–80%), while younger adults also adopted elevating strategies. Simulations showed that, when perturbed later in swing, a larger recovery step and higher recovery limb force were required for successful recovery.Interpretation: We suggested that a combination of insufficient recovery limb strength, response time and movement speed make it difficult for older adults to achieve a large enough recovery step for a successful elevating strategy recovery when perturbed later in mid-swing.

Gender-specific neuromuscular activity of the M. peroneus longus in healthy runners — A descriptive laboratory study - Corrected Proof

Heiner Baur, Anja Hirschmüller, Michael Cassel, Steffen Müller, Frank Mayer — 2010-07-26

Abstract: Background: Gender-specific neuromuscular activity for the ankle (e.g., peroneal muscle) is currently not known. This knowledge may contribute to the understanding of overuse injury mechanisms. The purpose was therefore to analyse the neuromuscular activity of the peroneal muscle in healthy runners.Methods: Fifty-three male and 54 female competitive runners were tested on a treadmill at 3.33ms−1. Neuromuscular activity of the M. peroneus longus was measured by electromyography and analysed in the time domain (onset of activation, time of maximum of activation, total time of activation) in % of stride time in relation to touchdown (=1.0). Additionally, mean amplitudes for the gait cycle phases preactivation, weight acceptance and push-off were calculated and normalised to the mean activity of the entire gait cycle.Findings: Onset of activation (mean; female: 0.86/male: 0.90, p<0.0001) and time of maximum of activation (female: 1.13/male: 1.16, p<0.0001) occurred earlier in female compared to male and the total time of activation was longer in women (female: 0.42/male: 0.39, p=0.0036). In preactivation, women showed higher amplitudes (+21%) compared to men (female: 1.16/male: 0.92, p<0.0001). Activity during weight acceptance (female: 2.26/male: 2.41, p=0.0039) and push-off (female: 0.93/male: 1.07, p=0.0027) were higher in men.Interpretation: Activation strategies of the peroneal muscle appear to be gender-specific. Higher preactivation amplitudes in females indicate a different neuromuscular control in anticipation of touchdown (“pre-programmed activity”). These data may help interpret epidemiologically reported differences between genders in overuse injury frequency and localisation.

A biomechanical model for estimating loads on thoracic and lumbar vertebrae - Corrected Proof

2010-07-26

Abstract: Background: Biomechanical models are commonly used to estimate loads on the spine. Current models have focused on understanding the etiology of low back pain and have not included thoracic vertebral levels. Using experimental data on the stiffness of the thoracic spine, ribcage, and sternum, we developed a new quasi-static stiffness-based biomechanical model to calculate loads on the thoracic and lumbar spine during bending or lifting tasks.Methods: To assess the sensitivity of the model to our key assumptions, we determined the effect of varying ribcage and sternal stiffness, maximum muscle stress, and objective function on predicted spinal loads. We compared estimates of spinal loading obtained with our model to previously reported in vivo intradiscal pressures and muscle activation patterns.Findings: Inclusion of the ribs and sternum caused an average decrease in vertebral compressive force of 33% for forward flexion and 18% in a lateral moment task. The impact of maximum muscle stress on vertebral force was limited to a narrow range of values. Compressive forces predicted by our model were strongly correlated to in vivo intradiscal pressure measurements in the thoracic (r=0.95) and lumbar (r=1) spine. Predicted trunk muscle activity was also strongly correlated (r=0.95) with previously published EMG data from the lumbar spine.Interpretation: The consistency and accuracy of the model predictions appear to be sufficient to justify the use of this model for investigating the relationships between applied loads and injury to the thoracic spine during quasi-static loading activities.

Ankle range of motion is key to gait efficiency in adolescents with cerebral palsy - Corrected Proof

Laurent Ballaz, Suzanne Plamondon, Martin Lemay — 2010-07-26

Abstract: Background: Gait in young people with cerebral palsy is inefficient and there is a lack of relevant indicators for monitoring the problem. In particular, the impact of gait kinematics on gait efficiency is not well documented. The aim of this study is to examine the relationship between gait efficiency, gait kinematics, lower limb muscle strength, and muscular spasticity in adolescents with cerebral palsy.Methods: Ten ambulatory adolescents with spastic cerebral palsy were recruited. The energy expenditure index during gait, gait kinematics, flexion and extension knee isometric muscle strength, and quadriceps spasticity were assessed.Findings: Energy expenditure index (1.5 (0.7) beats/m) was strongly correlated with the ankle and knee flexion/extension ranges of motion (r= −0.82, P<0.01 and r= −0.70, P<0.02, respectively) and also with maximal plantar flexion (r=0.74, P<0.05) during gait. Knee flexion strength was the only strength measurement correlated with energy expenditure index (r= −0.85; P<0.01).Interpretation: This study suggests that ankle and knee flexion/extension ranges of motion during gait are key kinematics factors in gait efficiency in adolescents with cerebral palsy.

Biomechanical effects of the extent of sacrectomy on the stability of lumbo-iliac reconstruction using iliac screw techniques: What level of sacrectomy requires the bilateral dual iliac screw technique? - Corrected Proof

2010-07-26

Abstract: Background: Although both single and dual iliac screw techniques are used in spino-pelvic reconstruction following sacrectomy for treating sacral tumors, the basis for choosing between the two techniques for different instability types remains undetermined. The purpose of this study was to evaluate the effects of the extent of sacrectomy on the stability of the lumbo-iliac fixation construct using single and dual iliac screw techniques.Methods: Nine human L2-pelvic specimens were tested for their intact condition simulated by L3–L5 pedicle screw fixation. Sequential partial sacrectomies and L3-iliac fixation using bilateral single and dual iliac screws were conducted on the same specimens as follows: under-S1 sacrectomy+single screw, under-½S1 sacrectomy+single screw, one-side sacroiliac joint resection+single screw, total sacrectomy+single screw, and total sacrectomy+dual screw. Biomechanical testing was performed on a material testing machine for evaluating the stiffness of the L3-iliac fixation construct in compression and torsion.Findings: Single iliac screw technique was found to effectively restore the local stability in under-½S1 sacrectomy. However, it could not provide adequate stability for further resection of one-side sacroiliac joint in torsion and total sacrectomy in compression (P<0.05). On the other hand, dual iliac screw technique could restore the stability to the intact condition after total sacrectomy in both compression and torsion.Interpretation: The single iliac screw technique for L3-iliac fixation could effectively restore the local stability for under-½S1 sacrectomy. However, for instabilities of the under-½S1 sacrectomy with one-side sacroiliac joint resection or total sacrectomy, the dual iliac screw technique should be considered.

Redistribution of joint moments during walking in patients with drop-foot - Corrected Proof

Erik B. Simonsen, Lene M. Moesby, Lasse D. Hansen, Jonathan Comins, Tine Alkjaer — 2010-07-26

Abstract: Background: The purpose of the study was to analyze the distribution of net joint moments in the lower extremities in patients walking with a drop-foot compared to a group of healthy subjects. A drop-foot causes the patient to walk with a characteristic limp and it was hypothesized that the drop-foot could lead to increased loadings of one or more joints.Methods: Six patients and fourteen healthy subjects walked at a fixed speed over two recessed force platforms while the movements were recorded by six infrared cameras. Net joint moments were calculated by inverse dynamics.Findings: The patients showed an almost doubled peak knee extensor moment during the stance phase compared to healthy subjects. This was accompanied by an increased knee joint flexion. The increased extensor moment about the knee joint was found in both the affected and unaffected leg of the patients. This was accompanied by increased maximal knee joint flexion in both legs of the patients compared to the healthy subjects. Several additional differences were observed in joint moments and joint angles between the two groups and between the two legs of the patients.Interpretation: The increased knee joint extensor moment leads to increased joint loading, which potentially may lead to development of osteo-arthritis over the years. It is recommended that patients with a drop-foot are offered an ankle joint orthosis in an attempt to restore normal function of the ankle joint, which will most likely reduce the knee joint loadings.

Biomechanical evaluation of a new fixation technique for internal fixation of three-part proximal humerus fractures in a novel cadaveric model - Corrected Proof

2010-07-26

Abstract: Background: The optimal surgical treatment for displaced proximal humeral fractures is still controversial. A new implant for the treatment of three-part fractures has been recently designed. It supplements the existing Expert Humeral Nail with a locking plate. We developed a novel humeral cadaveric model and the existing implant and the prototype were biomechanically compared to determine their ability in maintaining interfragmentary stability.Methods: The bone mineral density of eight pairs of cadaveric humeri was assessed and a three-part proximal humeral fracture was simulated with a Greater Tuberosity osteotomy and a surgical neck wedge ostectomy. The specimens were randomly assigned to either treatment. A bone anchor simulated part of a rotator cuff tendon pulling on the Greater Tuberosity. Specimens were initially tested in axial compression and afterward with a compound cyclic load to failure. An optical 3D motion tracking system continuously monitored the relative interfragmentary movements.Findings: The specimen stabilized with the prototype demonstrated higher stiffness (P=0.036) and better interfragmentary stability (P values<0.028) than the contralateral treated with the existing implant. There was no correlation between the bone mineral density and any of the investigated variables.Interpretation: The convenience of this new IM-nail and locking plate assembly must be confirmed in vivo but the current study provides a biomechanical rationale for its use in the treatment of three-part proximal humeral fractures. The improved stability could be advantageous in particular when medial buttress is missing, even in osteoporotic bone.

Intra-abdominal pressure and abdominal wall muscular function: Spinal unloading mechanism - Corrected Proof

Ian A.F. Stokes, Mack G. Gardner-Morse, Sharon M. Henry — 2010-07-26

Abstract: Background: The roles of antagonistic activation of abdominal muscles and of intra-abdominal pressurization remain enigmatic, but are thought to be associated with both spinal unloading and spinal stabilization in activities such as lifting. Biomechanical analyses are needed to understand the function of intra-abdominal pressurization because of the anatomical and physiological complexity, but prior analyses have been over-simplified.Methods: To test whether increased intra-abdominal pressure was associated with reduced spinal compression forces for efforts that generated moments about each of the principal axis directions, a previously published biomechanical model of the spine and its musculature was modified by the addition of anatomically realistic three-layers of curved abdominal musculature connected by fascia to the spine. Published values of muscle cross-sectional areas and the active and passive stiffness properties were assigned. The muscle activations were calculated assuming minimized muscle stress and stretch for the model loaded with flexion, extension, lateral bending and axial rotation moments of up to 60Nm, along with intra-abdominal pressurization of 5 or 10kPa (37.5 or 75mmHg) and partial bodyweight (340N).Findings: The analysis predicted a reduction in spinal compressive force with increase in intra-abdominal pressurization from 5 to 10kPa. This reduction at 60Nm external effort was 21% for extension effort, 18% for flexion effort, 29% for lateral bending and 31% for axial rotation.Interpretation: This analysis predicts that intra-abdominal pressure produces spinal unloading, and shows likely muscle activation patterns that achieve this.

Carpal tunnel pressure measurement during two-portal endoscopic carpal tunnel release - Corrected Proof

S. Uchiyama, T. Yasutomi, T. Momose, H. Nakagawa, M. Kamimura, H. Kato — 2010-07-26

Abstract: Background: Although there remain concerns of median nerve damage during endoscopic carpal tunnel release for carpal tunnel syndrome, carpal tunnel pressure variations during Chow's two-portal techinique have not been well investigated.Methods: We performed a modified two-portal endoscopic carpal tunnel release on 30 patients by inserting a catheter pressure transducer into the carpal tunnel for continuous pressure measurement during the procedure. Grip and pinch strengths, Semmes–Weinstein monofilament test, and nerve conduction studies were examined preoperatively and at postoperative 1, 3, and 6months. Numbness and the Disabilities of the Arm, Shoulder and Hand score were also evaluated pre and postoperatively.Findings: Subjective symptoms and nerve conduction study findings improved uneventfully. The pressure was always observed to be maximum pressure immediately before the cannula was withdrawn from the exit portal, and carpal tunnel pressure >300mmHg was recorded in most of the patients.Interpretation: A transient increase in the carpal tunnel pressure occurred in all the patients; however, it did not correlate with their clinical outcome or with increased risk of peri-operative complications. Since time–pressure threshold of the median nerve during endoscopic carpal tunnel release is still unknown, our results did not guarantee its safety.

Femoral component placement changes soft tissue balance in posterior-stabilized total knee arthroplasty - Corrected Proof

2010-07-26

Abstract: Background: We developed a new tensor for total knee arthroplasty enabling the soft tissue balance measurement after femoral trial placement with the patello-femoral joint reduced. The purpose of the present study is to compare the measurements of joint gap and ligament balance between osteotomized femoral and tibial surfaces in posterior-stabilized total knee arthroplasty with that between surfaces of femoral trial component and tibial osteotomy.Methods: Using this tensor, the effect of femoral trial placement on the soft tissue balance was analyzed in 80 posterior-stabilized total knee arthroplasties for varus osteoarthritic knees. Both joint gap and varus ligament imbalance were measured with 40lb of joint distraction force at extension and flexion, and compared between before and after femoral trial placement.Findings: In assessing the joint gap, there was significant decrease as much as 5.3mm at extension, not flexion, after femoral trial prosthesis placement. Varus ligament imbalances were significantly reduced with 3.1° at extension and increased with 1.2° in average at flexion after femoral trial placement.Interpretation: These changes at extension were caused by tensed posterior structures of the knee with the posterior condyle of the externally rotated aligned femoral trial. At the knee flexion, medial tension in the extensor mechanisms might be increased after femoral trial placement with patello-femoral joint repaired, and increased varus imbalance. Accordingly, we conclude that intensive medial release before femoral component placement to obtain rectangular joint gap depending on the conventional osteotomy gap measurement has a possible risk of medial looseness after total knee arthroplasty.

Effect of undersizing on the long-term stability of the Exeter hip stem: A comparative in vitro study - Corrected Proof

2010-07-26

Abstract: Background: Even for clinically successful hip stems such as the Exeter-V40 occasional failures are reported. It has been reported that sub-optimal pre-operative planning, leading to implant undersizing and/or thin cement mantle, can explain such failures. The scope of this study was to investigate whether stem undersizing and a thin cement mantle are sufficient to cause implant loosening.Methods: A comparative in vitro study was designed to compare hip implants prepared with optimal and smaller than optimal stem size. Exeter-V40, a highly polished cemented hip stem, was used in both cases. Tests were carried out simulating 24years of activity of active hip patients. A multifaceted approach was taken: inducible and permanent micromotions were recorded throughout the test; cement micro-cracks were quantified using dye penetrants and statistically analyzed.Findings: The implants with an optimal stem size withstood the entire mechanical test, with low and stable inducible micromotions and permanent migrations during the test, and with moderate fatigue damage in the cement mantle after test completion. Conversely, the undersized specimens showed large and increasing micromotions, and failed after few loading cycles, because of macroscopic cracks in the proximal part of the cement mantle. While results for the optimal stem size are typical for stable hip stems, those for the undersize stem indicate a critical scenario.Interpretation: These results confirm that even a clinically successful hip prosthesis such as the Exeter-V40 is prone to early loosening if a stem smaller than the optimal size is implanted.

Lower-limb adaptation during squatting after isolated posterior cruciate ligament injuries - Corrected Proof

Mei-Fang Liu, Pei-His Chou, Lih-Jiun Liaw, Fong-Chin Su — 2010-07-23

Abstract: Background: While many studies point out that posterior cruciate ligament plays an important role in squatting, not many, if any, have looked into knee kinematics or kinetics for isolated posterior cruciate ligament injuries. This study explores lower-limb adaptation during squatting for asymptomatic patients with isolated chronic posterior cruciate ligament injuries.Methods: Thirteen research subjects or test participants with isolated chronic posterior cruciate ligament injuries were recruited to analyze the kinematics and kinetics on both sides of their hip, knees and ankle joints during squatting. We adopted ExpertVision™ motion analysis system and two Kistler force plates to record the three-dimensional trajectories of the reflective markers used and the ground reaction forces respectively.Findings: The peak vertical ground reaction force exerted on the participants, their peak support moment and the knee-joint peak extension moment exhibited at their non-involved side are significantly greater than that at their involved side. We also find that the involved side's knee joint (extension moment) exhibits a reduced percentage on the peak support moment contributed by the individual joints, while the joints of the hip and ankle signify increased percentages.Interpretation: In this study, the asymptomatic participants having isolated chronic posterior cruciate ligament injuries tend to shift their weight to their non-involved side, and part of their injured knee-joint load to their ipsilateral joints of the hip and ankle. The causes seem to be a habitual gravity center shift, insufficient muscle strength at the involved side, and a reduced mechanical efficiency in their extensor mechanism.

Contribution of knee adduction moment impulse to pain and disability in Japanese women with medial knee osteoarthritis - Corrected Proof

2010-07-22

Abstract: Background: An increase in the knee adduction moment is one of the risk factors of medial knee osteoarthritis. This study examined the relationship between knee adduction moment and self-reported pain and disability. We also investigated the influence of pain on the relationships between knee adduction moment and gait performance and disability.Methods: Thirty-eight Japanese women with medial knee osteoarthritis participated in this study (66.37years (41–79years)). Gait analysis involved the measurement of the external knee adduction moment impulse in the stance duration and during 3 subdivisions of stance. The total, pain and stiffness, and physical function Japanese Knee Osteoarthritis Measure scores were determined.Findings: The pain and stiffness, physical function, and total scores were positively correlated with the knee adduction moment impulses in the stance duration, and initial and second double support interval, and single limb support interval. The knee adduction moment impulse during the stance duration was related to the pain and stiffness subscale and gait velocity. The pain and stiffness subscale was related to the physical function subscale.Interpretation: Our results suggest that increasing in the knee adduction moment impulse, a proxy for loading on the medial compartment of the knee, is related to increased pain during weight-bearing activities such as walking, thereby restricting walking performance and causing disability by reducing gait velocity. Thus, the reduction in the knee adduction moment impulse during gait may result in pain relief and may serve as a conservative treatment option with disease-modifying potential.

APOS therapy improves clinical measurements and gait in patients with knee osteoarthritis - Corrected Proof

2010-07-20

Abstract: Background: The purpose of the study was to investigate the changes in gait patterns and clinical measurements following treatment with a novel biomechanical device on patients with knee osteoarthritis.Methods: Forty six patients with bilateral knee osteoarthritis were analyzed. Patients completed a gait test, Western Ontario and McMaster Osteoarthritis Index (WOMAC) questionnaire and SF-36 Health Survey at baseline and after 12weeks. The biomechanical device was individually calibrated to each patient at baseline to allow training under reduced pain.Findings: Gait velocity, step length and single limb support improved significantly and toe out angle decreased significantly (10%, 6%, 1% and 2%, respectively). WOMAC-Pain and WOMAC-Function significantly decreased (26% and 34%, respectively), and SF-36 score significantly increased following the 12weeks of treatment.Interpretation: Our results suggest an overall improvement in the gait patterns, level of pain and level of function of patients with knee osteoarthritis following 12weeks of treatment with the novel biomechanical device.The study is registered at clinicaltrials.gov, identifier NCT00767780, http://www.clinicaltrials.gov/ct/show/NCT00767780.